Eric Raymond, in “How to Become a Hacker“, recommended five languages: C, Java, Python, Perl, and Lisp. Each he recommended for different reasons: Python and Java as introductory languages, C to understand and hack Unix, Perl because of its use in scripting, and Lisp for, to use his words which are so much better than anything I can come up with, the profound enlightenment experience you will have when you finally get it. That experience will make you a better programmer for the rest of your days, even if you never actually use LISP itself a lot.

It’s 2012. Many languages have come to the fore that didn’t exist when this essay was written. Others, like Perl, have faded somewhat. What is today’s five-language list? I won’t pretend that my answer is necessarily the best; it’s biased based on what I know. That said, I’d think the 5 highest-return languages for people who want to become good engineers are the following, and in this order: Python, C, ML, Clojure, and Scala.

Why these 5? Python I include because it’s easy to learn and, in-the-small, extremely legible. I’d rather not use it for a large system, but people who are just now learning to program are not going to be writing huge systems. They’re not going to be pushing major programs into production. At least, they shouldn’t be. What they should be able to do is scrape a webpage or build a game or investigate an applied math problem and say, “Shit, that’s cool.” Python gets people there quickly. That will motivate them to get deeper into programming. Python is also a language that is not great at many things, but good at one hell of a lot of them. It’s quick to write, legible in the small, and expressive. It allows imperative and functional styles. It has great libraries, and it has strong C bindings, for when performance is needed.

People who are getting started in programming want to do things that are macroscopically interesting from a beginner’s perspective. They don’t just want to learn about algorithms and how compilers work, because none of that’s interesting to them until they learn more of the computer science that motivates the understanding of why these things are important. Compilers aren’t interesting until you’ve written programs in compiled languages. At the start, people want to be able to write games, scrape webpages, and do simple systems tasks that come up. Python is good because it’s relatively easy to do most programming tasks in it.

After Python, C is a good next choice, and not because of its performance. That’s largely irrelevant to whether it will make someone a better programmer (although the confidence, with regard to understanding performance, that can come with knowing C is quite valuable). C is crucial because there’s a lot of computer science that becomes inaccessible if one sticks to higher-level languages (and virtual machines) like Java, C#, and Python. Garbage collection is great, but what is the garbage collector written in? C. As is Unix, notably. For all this, I think C is a better choice than C++ because there’s another important thing about C: C++ is a mess and it’s not clear whether it’s a good language for more than 1% of the purposes to which it’s put, but C, on the other hand, has utterly dominated the mid-level language category. For all its flaws, C is (like SQL for database query languages) a smashing, undisputed success, and for good reasons. The high-level language space is still unsettled, with no clear set of winners, but the mid–level language used to write the runtimes and garbage collectors of those high level languages is usually C, and will be for some time.

Python and C give a person coverage of the mid- and very-high levels of language abstraction. I’m avoiding including low-level (i.e. assembly) languages because I don’t think any of them have the generalist’s interest that would justify top-5 placement. Familiarity with assembly language and how it basically works is a must, but I don’t think mastery of x86 intricacies is necessary for most programmers.

Once a programmer’s fluent in Python and C, we’re talking about someone who can solve most coding problems, but improvement shouldn’t end there. Taste is extremely important, and it’s lack of taste rather than lack of intellectual ability that has created the abundance of terrible code in existence. Languages can’t inherently force people to learn taste, but a good starting point in this direction is ML: SML or OCaml with the “O” mostly not used.

ML has been described as a “functional C” for its elegance. It’s fast, and it’s a simple language, but its strong functional programming support makes it extremely powerful. It also forces people to program from the bottom up. Instead of creating vague “objects” that might be hacked into bloated nonsense over the lifespan of a codebase, they create datatypes (mostly, records and discriminated unions, with parameterized types available for polymorphism) out of simpler ones, and use referentially transparent functions as the basic building blocks of most of their programs. This bottom-up structure forces people to build programs on sound principles (rather than the vague, squishy abstractions of badly-written object-oriented code) but ML’s high-level capability brings people into the awareness that one can write complex software using a bottom-up philosophy. Python and C teach computer science at higher and lower levels, but ML forces a programmer to learn how to write good code.

There’s also something philosophical that Python, C, and Ocaml tend to share that C++ and Java don’t: small-program philosophy, which is generally superior. I’ve written at length about the perils of the alternative. In these languages, it’s much more uncommon to drag in the rats’ nest of dependencies associated with large Java projects. For an added bonus, you never have to look at those fucking ugly singleton directories called “com”. Once a person has used these three languages to a significant extent, one gets a strong sense of how small-program development works and why immodular, large-project orientation is generally a bad thing.

When you write C or Ocaml or Python, you get used to writing whole programs that accomplish something. There’s a problem, you solve it, and you’re done. Now you have a script, or a library, or a long-running executable. You may come back to it to improve it, but in general, you move on to something else, while the solution you’ve created adds to the total stored value of your code repository. That’s what’s great about small-program development: problems are actually solved and work is actually “done” rather than recursively leading to more work without any introspection on whether the features being piled on the work queue make sense. Developers who only experience large-program development– working on huge, immodular Java projects in IDEs a million metaphorical miles from where the code actually runs for real– never get this experience of actually finishing a whole program.

Once a person has grasped ML, we’re talking about a seriously capable programmer, even though ML isn’t a complex language. Learned in the middle of one’s ML career is a point to which I’ll return soon, but for now leave hanging: types are interesting. One of the most important things to learn from ML is how to use the type system to enforce program correctness: it generates a massive suite of implicit unit tests that (a) never have to be written, and (b) don’t contribute to codebase size. (Any decent programmer knows that “lines of code” represent expenditure, not accomplishment.)

The fourth language to learn is Clojure, a Lisp that happens to run on the JVM. The JVM has its warts, but it’s powerful and there are a lot of good reasons to learn that ecosystem, and Clojure’s a great entry point. A lot of exciting work is being done in the JVM ecosystem, and languages like Clojure and Scala keep some excellent programmers interested in it. Clojure is an excellent Lisp, but with its interactive “repl” (read-eval-print-loop) and extremely strong expressivity, it is (ironically)  arguably the best way to learn Java. It has an outstanding community, a strong feature set, and some excellent code in the open-source world.

Lisp is also of strong fundamental importance, because its macro system is unlike anything else in any other language and will fundamentally alter how an engineer thinks about software, and because Lisp encourages people to use a very expressive style. It’s also an extremely productive language: large amounts of functionality can be delivered in a small amount of time. Lisp is a great language for learning the fundamentals of computing, and that’s one reason why Scheme has been traditionally used in education. (However, I’d probably advocate starting with Python because it’s easier to get to “real stuff” quickly in it. Structure and Interpretation of Computer Programs and Scheme should be presented when people know they’re actually interested in computing itself.)

When one’s writing large systems, Lisp isn’t the best choice, because interfaces matter at that point, and there’s a danger that people will play fast-and-loose with interfaces (passing nested maps and lists and expecting the other side to understand the encoding) in a way that can be toxic. Lisp is great if you trust the developers working on the project, but (sadly) I don’t think many companies remain in such a state as they grow to scale.

Also, static typing is a feature, not a drawback. Used correctly, static typing can make code more clear (by specifying interfaces) and more robust, in addition to the faster performance usually available in compiled, statically typed languages. ML and Haskell (which I didn’t list, but it’s a great language in its own right) can teach a person how to use static typing well.

So after Lisp, the 5th language to master is Scala. Why Scala, after learning all those others, and having more than enough tools to program in interesting ways? First of all, it has an incredible amount of depth in its type system, which attempts to unify the philosophies of ML and Java and (in my opinion) does a damn impressive job. The first half of Types and Programming Languages is, roughly speaking, the theoretic substrate for ML. But ML doesn’t have a lot of the finer features. It doesn’t have subtyping, for example. Also, the uniqueness constraint on record and discriminated union labels (necessary for full Hindley-Milner inference, but still painful) can have a negative effect on the way people write code. The second half of TAPL, which vanilla ML doesn’t really support, is realized in Scala. Second, I think Scala is the language that will salvage the 5 percent of object-oriented programming that is actually useful and interesting, while providing such powerful functional features that the remaining 95% can be sloughed away. The salvage project in which a generation of elite programmers selects what works from a variety of programming styles– functional, object-oriented, actor-driven, imperative– and discards what doesn’t work, is going to happen in Scala. So this is a great opportunity to see first-hand what works in language design and what doesn’t.

Scala’s a great language that also requires taste and care, because it’s so powerful. I don’t agree with the detractors who claim it’s at risk of turning into C++, but it definitely provides enough rope for a person to hang himself by the monads.

What’s most impressive about Clojure and Scala is their communities. An enormous amount of innovation, not only in libraries but also in language design, is coming out of these two languages. There is a slight danger of Java-culture creep in them, and Scala best practices (expected by the leading build environments) do, to my chagrin, involve directories called “src” and “main” and even seem to encourage singleton directories called “com”, but I’m willing to call this a superficial loss and, otherwise, the right side seems to be winning. There’s an incredible amount of innovation happening in these two languages that have now absorbed the bulk of the top Java developers.

Now… I mentioned “six languages” in this post’s title but named five. The sixth is one that very few programmers are willing to use in source code: English. (Or, I should say, the scientifically favored natural language of one’s locale.) Specifically, technical English, which requires rigor as well as clarity and taste. Written communication. This is more important than all of the others. By far. For that, I’m not complaining that software engineers are bad at writing. Competence is not a problem. Anyone smart enough to learn C++ or the finer points of Lisp is more than intelligent enough to communicate in a reasonable way. I’m not asking people to write prose that would make Faulkner cry; I’m asking them to explain the technical assets they’ve created at, at the least, the level of depth and rigor expected in a B+ undergraduate paper. The lack of writing in software isn’t an issue of capability, though, but of laziness.

Here’s one you hear sometimes: “The code is self-documenting.” Bullshit. It’s great when code can be self-documenting, making comments unnecessary, but it’s pretty damn rare to be solving a problem so simple that the code responsible for solving it is actually self-explanatory. Most problems are custom problems that require documentation of what is being solved, why, and how. People need to know, when they read code, what they’re looking at; otherwise, they’re going to waste a massive amount of time focusing on details that aren’t relevant. Documentation should not be made a crutch– you should also do the other important things like avoiding long functions and huge classes– but it is essential to write about what you’re doing. People need to stop thinking about software as machinery that “explains itself” and start thinking of it as writing a paper, with instructions for humans about what is happening alongside the code actually doing the work.

One of the biggest errors I encounter with regard to commenting is the tendency to comment minutiae while ignoring the big picture. There might be a 900-line program with a couple comments saying, “I’m doing this it’s O(n) instead of O(n^2)” or “TODO: remove hard-coded filename”, but nothing that actually explains why these 900 lines of code exist. Who does that help? These types of comments are useless to people who don’t understand what’s happening at all, which they generally won’t in the face of inadequate documentation. Code is much easier to read when one knows what one is looking at, and microcomments on tiny details that seemed important when the code was written are not helpful.

Comments are like static typing: under-regarded if not ill-appreciated because so few people use them properly, but very powerful (if used with taste) in making code and systems actually legible and reusable. Most real-world code, unfortunately, isn’t this way. My experience is that about 5 to 10 percent of code in a typical codebase is legible, and quite possibly only 1 percent is enjoyable to read (which good code truly is). The purpose of a comment should not be only to explain minutiae or justify weird-looking code. Comments should also ensure that people always know what they’re actually looking at.

The fallacy that leads to a lack of respect for documentation is that writing code is like building a car or some other well-understood mechanical system. Cars don’t come with a bunch of labels on all the pieces, because cars are fairly similar under the hood and a decent mechanic can figure out what is what. With software, it’s different. Software exists to solve a new problem; if it were solving an old problem, old software could be used. Thus, no two software solutions are going to be the same. In fact, programs tend to be radically different from one another. Software needs to be documented because every software project is inherently different, at least in some respects, from all the others.

There’s another problem, and it’s deep. The 1990s saw an effort, starting with Microsoft’s visual studio, to commoditize programmers. The vision was that, instead of programming being a province of highly-paid, elite specialists with a history of not working well with authority, software could be built by bolting together huge teams of mediocre, “commodity” developers, and directing them using traditional (i.e. pre-Cambrian) management techniques. This has begun to fail, but not before hijacking object-oriented programming, turning Java’s culture poisonous, and creating some of the most horrendous spaghetti code (MudballVisitorFactoryFactory) the world has ever seen. Incidentally, Microsoft is now doing a penance by having its elite research division investigate functional programming in a major way, the results being F# and a much-improved C#. Microsoft, on the whole, may be doomed to mediocrity, but they clearly have a research division that “gets it” in an impressive way. Still, that strikes me as too little, too late. The damage has be done, and the legacy of the commodity-developer apocalypse still sticks around.

The result of the commodity-programmer world is the write-only code culture that is the major flaw of siloized, large-program development. That, I think, is the fundamental problem with Java-the-culture, IDE-reliance, and the general lack of curiosity observed (and encouraged) among the bottom 80 percent of programmers. To improve as programmers, people need to read code and understand it, in order to get a sense of what good and bad code even are, but almost no one actually reads code anymore. IDEs take care of that. I’m not going to bash IDEs too hard, because they’re pretty much essential if you’re going to read a typical Java codebase, but IDE culture is, on the whole, a major fail that makes borderline-employable programmers out of people who never should have gotten in in the first place.

Another problem with IDE culture is that the environment becomes extremely high maintenance, between plugins that often don’t work well together, build system idiosyncracies that accumulate over time, and the various menu-navigation chores necessary to keep the environment sane (as opposed to command-line chores, which are easily automated). Yes, IDEs do the job: bad code becomes navigable, and commodity developers (who are terrified of the command line and would prefer not to know what “build systems” or “version control” even are) can crank out a few thousand lines of code per year. However, the high-maintenance environment requires a lot of setup work, and I think this is culturally poisonous. Why? For a contrast, in the command-line world, you solve your own problems. You figure out how to download software (at the command line using wget, not clicking a button) and install it. Maybe it takes a day to figure out how to set up your environment, but once you’ve suffered through this, you actually know a few things (and you usually learn cool things orthogonal to the problem you were originally trying to solve). When a task gets repetitive, you figure out how to automate it. You write a script. That’s great. People actually learn about the systems they’re using. On the other hand, in IDE-culture, you don’t solve your own problems because you can’t, because there it would take too long. In the big-program world, software too complex for people to solve their own problems is allowed to exist. Instead of figuring it out on your own, you flag someone down who understands the damn thing, or you take a screenshot of the indecipherable error box that popped up and send it to your support team. This is probably economically efficient from a corporate perspective, but it doesn’t help people become better programmers over time.

IDE culture also creates a class of programmers who don’t work with technology outside of the office– the archetypal “5:01 developers”– because they get the idea that writing code requires an IDE (worse yet, an IDE tuned exactly in line with the customs of their work environment). If you’re IDE-dependent, you can’t write code outside of a corporate environment, because when you go home, you don’t have a huge support team to set the damn thing up in a way that you’re used to and fix things when the 22 plugins and dependencies that you’ve installed interact badly.

There are a lot of things wrong with IDE culture, and I’ve only scratched the surface, but the enabling of write-only code creation is a major sticking point. I won’t pretend that bad code began with IDEs because that’s almost certainly not true. I will say that the software industry is in a vicious cycle, which the commodity-developer initiative exacerbated. Because most codebases are terrible, people don’t read them. Because “no one reads code anymore”, the bulk of engineers never get better, and continue to write bad code.

Software has gone through a few phases of what it means for code to actually be “turned in” as acceptable work. Phase 1 is when a company decides that it’s no longer acceptable to horde personal codebases (that might not even be backed up!) and mandates that people check their work into version control. Thankfully, almost all companies have reached that stage of development. Version control is no longer seen as “subversive” by typical corporate upper management. It’s now typical. The second is when a company mandates that code have unit tests before it can be relied upon, and that a coding project isn’t done until it has tests. Companies are reaching this conclusion. The third milestone for code-civilizational development, which very few companies have reached, is that the code isn’t done until you’ve taught users how to use it (and how to interact with it, i.e. instantiate the program and run it or send messages to it, in a read-eval-print-loop appropriate to the language). That teaching can be supplied at a higher level in wikis, codelabs, and courses… but it also needs to be included with the source code. Otherwise, it’s code out-of-context, which becomes illegible after a hundred thousand lines or so. Even if the code is otherwise good, out-of-context code without clear entry-points and big-picture documentation becomes incomprehensible around this point.

What do I not recommend? There’s no language that I’d say is categorically not worth learning, but I do not recommend becoming immersed in Java (except well enough to understand the innards of Clojure and Scala). The language is inexpressive, but the problem isn’t the language, and in fact I’d say that it’s unambiguously a good thing for an engineer to learn how the JVM works. It’s that Java-the-Culture (VisitorSelectionFactories, pointless premature abstraction, singleton directories called “com” that betray dripping contempt for the command line and the Unix philosophy, and build environments so borked that it’s impossible not to rely on an IDE) that is the problem; it’s so toxic that it reduces an engineer’s IQ by 2 points per month.

For each of these five programming languages, I’d say that a year of exposure is ideal and probably, for getting a generalist knowledge, enough– although it takes more than a year to actually master any of these. Use and improvement of written communication, on the other hand, deserves more. That’s a lifelong process, and far too important for a person not to start early on. Learning new programming languages and, through this, new ways of solving problems, is important; but the ability to communicate what problem one has solved is paramount.